1. Field of the Invention
The present invention relates to an adsorption sheet and a method for making the same, and more particularly, to a composite adsorption sheet for mounting a workpiece and a method for making the same.
2. Description of the Related Art
Polishing generally refers to abrasion control of an originally rough surface in a chemical mechanical polishing (CMP) process, in which a slurry containing fine particles is uniformly distributed on an upper surface of a polishing pad, and a polishing workpiece is pressed against the polishing pad to be polished regularly in a repeated pattern. The polishing workpiece is, for example, semiconductor, storage medium substrate, integrated circuit, LCD flat panel glass, optical glass, and photoelectric panel. During the polishing, it is necessary to use a sheet to support and mount the polishing workpiece, and the quality of the sheet directly affects the polishing effect of the polishing workpiece.
FIG. 1 is a schematic diagram of a polishing equipment having a conventional sheet disclosed in U.S. Pat. No. 5,871,393. The polishing equipment 1 includes a lower base plate 11, a sheet 12, a polishing workpiece 13, an upper base plate 14, a polishing pad 15, and slurry 16. The lower base plate 11 is opposite to the upper base plate 14. The sheet 12 is adhered onto the lower base plate 11 with a back adhesive layer 17, and is used to support and mount the polishing workpiece 13. The polishing pad 15 is mounted on the upper base plate 14 and facing the lower base plate 11, for polishing the polishing workpiece 13.
The polishing equipment 1 operates as follows. Firstly, the polishing workpiece 13 is disposed on the sheet 12, and is adsorbed by the sheet 12. Next, the upper base plate 14 and the lower base plate 11 are rotated in opposite directions, and meanwhile, the upper base plate 14 moves downward, so as to make the polishing pad 15 contact the surface of the polishing workpiece 13. In this way, the polishing workpiece 13 is polished by continuously supplementing the slurry 16 together with the function of the polishing pad 15.
FIG. 2 is a schematic enlarged diagram of region A in FIG. 1. The region A mainly shows the sheet 12. The sheet 12 is a single-layered structure, and the material thereof is generally polyurethane (PU) resin, which is a foam material. Furthermore, the sheet 12 has a plurality of communicating foam pores 121 inside.
During the polishing process, the polishing workpiece 13 and the sheet 12 bear a downward pressure, and the compression ratio of the sheet 12 may affect the overall stress uniformity, which is also a critical factor in determining the flatness of the polishing workpiece 13 after being polished. That is, high compression ratio represents good buffer effect, such that the polishing workpiece 13 after the polishing may acquire good flatness. In general, after long-term usage, the compression ratio of the sheet 12 will gradually descend to end the life of the sheet 12.
As the sheet 12 is a single-layer structure, if the material thereof is soft, though the adsorption to the polishing workpiece 13 is strong, the compression ratio is low; while if the material thereof is hard, though the compression ratio is high, the adsorption to the polishing workpiece 13 is weak.
Therefore, it is necessary to provide a composite sheet for mounting a workpiece and a method for making the same to solve the above problems.